Environmental load reductions in transportation systems are essential for a sustainable society. In this study, a life cycle simulation model was developed for a transportation system including automobiles and public transportation. Life cycle simulation is a method for evaluating an environmental load of a product through its life cycle. To focus on total transportation demand and their teardown, effects by a temporal change of population pyramid were considered. We modeled this demand change of transportation and reflected it to life cycle simulation model. A case study was conducted on the transportation system including automobiles, buses, and trains in Suita, Osaka. The total amount of CO2 emission and total material requirement were calculated over the next 25 years.